The present invention relates generally to improvements in adjustable aperture lens diaphragms and it relates particularly to an interchangeable objective lens with an improved automatic preset aperture diaphragm.
A prior art diaphragm mechanism of the subject type is disclosed in U.S. Pat. No. 3,165,997 issued on Jan. 19, 1965. While this prior art mechanism is highly satisfactory it possesses certain drawbacks. Although the aforesaid mechanism is described in detail in the above patent an explanation thereof will provide a better understanding of the improved mechanism.
Referring to FIGS. 1 and 3 of the present drawings which illustrate a prior art mechanism, a reciprocating lever 1 in a camera body (not shown) is displaced or advanced from an initial or retracted position in the direction of the arrow prior to the commencement of an exposure sequence and returns to its initial position in response to the completion of the exposure sequence. The reciprocating lever 1 is brought into contact with a follower or engaging piece 2 of an arcuate diaphragm actuating lever 3 which is pivoted about an axis 4 to the lens barrel or cylinder which can be detachably mounted to the camera body by means of a coupling portion 25a and which is biased by a spring 6 to rotate clockwise. An arcuate lever 5 overlapping lever 3 is provided at its middle portion with a stop pin 8 and proximate an end thereof with a fork or yoke portion 5a and is coaxially provided with axis 4 on diaphragm actuating lever 3. The levers 3 and 5 are intercoupled and embracingly energized by a spring 13; the other end portion 5b of the overlapping lever 5 proximate yoke 5a is brought into contact with a stop defining pin 7 secured to the diaphragm actuating lever 3. The stop pin 8 is brought into contact with a cam plate 9 secured to the diaphragm adjusting ring 17. Opposing the stationary side of diaphragm blades 20, is a diaphragm mounting or pushing ring 16 having holes 16a which rotatably receive respective pins from blades 21 and a diaphragm control rod or pin 11 is secured to the diaphragm driving ring 12 and actuates the diaphragm blades 20 and is engaged in the fork portion 5a of the overlapping lever 5. In this case, the diaphragm actuating pin 11 is of a sufficient length to prevent the pin 11 from disengaging fork portion 5a even when the helicoid 27 is extended for focusing.
In the above arrangement, when the camera shutter button (not shown) is depressed after the desired diaphragm value is preset by diaphragm adjusting ring 17, the reciprocating lever 1 moves in the direction of the arrow through the known related mechanisms prior to the commencement of the exposure. Thus, the diaphragm actuating lever 3, which has been held in its initial posiition along with the engaging member 2 by the reciprocating lever 1, turns counter-clockwise about the pivot 4 under the influence of the spring 6 to similarly push and turn the overlapping lever 5 which in turn moves the diaphragm control pin 11 registering with the recess of the fork portion 5a and the diaphragm driving ring 12 carrying the control pin 11. The diaphragm blades 20 have respective elongated slots engaged by pins secured to the ring 12 and are accordingly stopped down from a full open position, reducing the aperture 30 formed thereby, with the blades 20 pivoting about the pins 21 engaging holes 16a of the pushing ring 16. The stop pin 8 of the overlapping lever 5 is advanced to and abuts against the periphery of the cam plate 9 which has been located at a selectively preset or predetermined position. Thus, the lever 5 is prevented from advancing further than the cam plate preset position, whereby diaphragm blades 20 are stopped automatically as its aperture size reaches to the preset desired value.
The reciprocating lever 1 returns in a direction opposite to that of the arrow, pushing back the diaphragm actuating lever 3 against the influence of the spring 6, after completion of the exposure with the lever 1 abutting the engaging member 2. The overlapping lever 5, following the lever 3 under the influence of spring 13, returns to its initial position. Thus, the diaphragm driving ring 12 causes the diaphragm blades 20 to return to its original fully open position through the diaphragm control pin 11 engaged by the fork portion 5a. A stop 12a is provided on the diaphragm opening ring 12 in order to prevent further rotation thereof from its fully open position.
The reciprocating lever 1 will somewhat further advance in the direction opposite to that of the arrow in order to return to its initial position and to bias the diaphragm aperture to the completely fully open condition. More particularly, the reciprocating lever 1 is further somewhat moved in the reverse direction to that of the arrow after the diaphragm aperture 30 reaches its fully open condition whereby the actuating lever 3 further rotates in a counterclockwise direction against the influence of the spring 6. The overlapping lever 5 tends to follow the actuating lever 3 under the action of spring 13 so as to further rotate the diaphragm driving ring 12 in counterclockwise direction beyond its fully open position, but such further movement of the overlapping lever 5 and the driving ring 12 are prevented by the stop 12a provided on the ring 12 engaging an abutment. Therefore, only the actuating lever 3 is further rotated counterclockwise, disengaging the pin 7 from the end portion 5b of the overlapping lever 5 and charging the spring 13, thereby providing a gap between the end portion 5b and the pin 7. In this state, as the diaphragm driving ring 12 is continuously urged in a counterclockwise direction by the spring 13, the diaphragm aperture 30 is maintained in its fully open condition.
In order to ensure the fully opened condition of the diaphragm aperture 30 when the stop 12a abuts the abutment defining stationary portion of the lens barrel, the diaphragm pushing ring 16 is rotatable so that its relative angular position with respect to the diaphragm driving ring 12 may be adjusted. Practically, the adjustment for ensuring a fully opened aperture is carried out in a manner that the diaphragm pushing ring 16 is rotated with the ring 12 being kept at a position where the stop 12a engages the stationary abutment.
As the above described conventional mechanism is so constructed as that the diaphragm driving ring 12 is positively or forcibly rotated in a counterclockwise direction through the engagement of the fork portion 5a and the diaphragm control pin 11 when the diaphragm adjusting ring 17 carrying cam plate 9 is rotated toward a position to preset the fully open diaphragm aperture value, the following shortcomings or defects may occur.
When the diaphragm adjusting ring 17 is erroneously set to a position for fully opening the aperture, before the above-mentioned adjustment for ensuring fully open aperture condition is completed, the driving ring 12 is forcibly rotated beyond a position where the pin 19 engages the rear edge 20a of the next blade 20. Thus, the diaphragm blades 20 may be damaged or deformed.
Further, even if the adjustment for ensuring the fully open aperture has been completed, an undesirable force may be exerted to rotate the diaphragm driving ring 12 beyond a position where the stop 12a engages the stationary abutment portion.
The diaphragm adjusting ring 17 is, in general, restricted in its angular rotation to a predetermined amount by a stop 18 which is secured to the stationary portion of the lens barrel and engages a groove 24 formed in the inner wall of the ring 17, as shown in FIG. 5.
The groove 24 and the stop 18 are not necessarily formed or manufactured to the exact dimensions as designed, thus, errors likely occur in the extend and size of the groove and the stop. Further, upon assembly, the stop 18 may be secured with some positional error relative to the groove to the stationary portion of the lens barrel.
Accordingly, as seen in FIG. 5, the diaphragm adjusting ring 17 may be further rotated counterclockwise for an angle a beyond a predetermined limit, due to the accumulation of such errors. When the diaphragm adjusting ring 17 is further rotated beyond its desired limit, the cam plate 9 depresses the stop pin 8 to undesirably rotate the overlapping lever 5 counterclockwise. Thus, as explained above, an excessive force may be exerted on the diaphragm driving ring 12 to unnecessarily rotate it counterclockwise.
When such excessive force is exerted on the diaphragm driving ring 12, the ring 12 may be deformed or distorted since ring 12 is generally constructed as a thin member for quick movement. As a result, with the structure of the conventional mechanism, a smooth operation for opening and closing the diaphragm aperture is obstructed.
The conventional mechanism of the above nature requires a large number of parts in order to transmit the movement of the diaphragm adjusting ring 17 to the diaphragm control pin 11. For instance, the cam means including cam plate 9 and stop pin 8, the actuating lever 3, the overlapping lever 5, and the spring 17 for cooperatively urging the actuating lever 3 and overlapping lever 5 are required. Moreover, with the conventional structure, the diaphragm actuating lever 3, the overlapping lever 5 and the diaphragm control pin 11 must be associated in particular interfitting relationship with each other in order to achieve the proper transmitting function.
As a result, the number of parts and the complexity in construction of the mechanism are increased, and their assembly is highly time consuming.